AbstractID: 1578 Title: Reproducibility of multislice spiral CT scans
For the image reconstruction of a CT scan at any position,
transmission measurements from all x--ray source angles are needed
at that position. At spiral CT missing projections are calculated
by means of interpolation, using measurements at positions nearby.
This procedure may lead to interpolation artifacts. The
relationship between the x-ray source angle and the spiral
reconstruction artifacts is investigated here. The angle of the
x-ray source at the starting scan position varies and can not be
chosen. The angle is only known after the scan has been made. We
determine and quantify the influence of this phenomenon on the
reproducibility of CT scans. Reproducible spiral CT scans are
required when image processing such as subtraction or masking is
used. We used a head phantom consisting of a human skull in a
synthetic material and a CT scanner with four detector arrays. We
made series of scans of the same region with all adjustable scan
parameters kept constant in order to obtain a collection of
different values for the starting x-ray source angle. Series were
made for different pitch values. We conclude that in general
images of a spiral CT scan are not reproducible. Only if the x-ray
source starting angle is equal for both scans or if a very low
pitch is used, images are highly reproducible. Under other
circumstances interpolation artifacts show up differently in
otherwise identical images, and show up as substantial residual
artifacts when for example subtractions are made.